Modulation



Dec. 23, 1941. Q HENKLER 2,267,703

MODULATION Filed Nov. l5, `1940 2 Sheets-Sheet 2 CONTROL PTEN T//L JOI/ECE :inventor BH M55/tw,

. Gttonug .Patented Dec. 23, 1941 MonULA'rIoN Otto Henkler,

Berlin,

Germany,

assignor to Fides Gesellschaft fr die Verwaltung und Verwertung von gewerblichen Schutzrechten mit beschrnkter Haftung, Berlin, Germany, a corporation of Germany Application November 15, 1940, Serial No. 365,745 In Germany October l2, 1939 5 Claims.

For modulation purposes the invention utilizes an amplifier which has been linearized (that is to say, in which non-linear distortionsare corrected) byv means of a negative feedback between the input and the output circuit. This amplifier may be regarded as amplifying one of the frequencies to be modulated with each other. The amplifier itself may consist of a cascade of ampliers. According to the invention, the damping occurring in the feedback path is controlled by the other one of the frequencies to be modulated with one another.

The basic principle of the invention shall now be described more fully by reference to the appended drawings, wherein:

Fig. 1 illustrates diagrammatically an embodiment of my modulation system. l

Fig. 2-is a curve showing the characteristic of a rectifier used in the system ;v while Figs. 3, 4, 5 and 6 are each modifications of my controlled degenerative feedback amplier of waves to be modulated.

In the-feedback path of amplier V for carrier frequency Q, having a gain So, is a network or mesh N of variable attenuation bR. The

negative feedback, as shown in the prior art, may

bepredicated upon a current or a voltage feedback, or else a combination of both. Attenuation bR and thus the gain Q?! s" U1 of the arrangement is subject lto control or modulator action occurring at the rhythm of voltage' Uw. U2 isthe output voltage, Ulis the carrier voltage and Uw is the modulation voltage. According to the amplitude of the signal frequency w, the attenuation of the network or mesh will be either raised or diminished. The carrier frequency voltage U2 arising in the output end of the amplifier, as will thus be seen, varies at the rate or rhythm of the signal and contains the de'- Y for several systems, especially where multiple generators are employed.

While the negative feedback varies it is always present, and as a result the properties of the ampliiier tube are improved as well known'in the art. More particularly, additional modulation in the tube as a result of its curvature is lessened.

It is known in the earlier art to utilize a plate current or amplifying detector for modulation purposes in which by negative feedback yand the use of tubes having a very low grid penetration factor a nearly ideally bent characteristic is obtained. However, because of the peculiarity inherent in this known arrangement, the gain is extremely low. The invention contradistinct therefrom discloses how to use the negative feedback network or mesh in a linearized amplifier for modulation purposes,.that is to say, the combination of a negative feedback amplifier with a modulator. In this way a high gain is securable,

while yet the necessary circuit means are not` dition:

:s inra" l), 1)

where S is the mutual conductance or slope of the amplifier tube, su is the gain of the amplifier V in the absence of negative feedback, s is the gain of the amplier tube with negative feedback. Uw is the amplitude of the controlling frequency w andjc the ratio between the output amplitude U2 and the control amplitude Uw. To satisfy the said condition it'would seem that the dry-type (oxide) rectifier, more especially copper-oxide' rectiers or combinations comprising the same is most suitable.

Fig. 2 shows the dependence of the resistance alternating amplitude Uw.

curve satisfies very closely the condition:

1 Uw 1+ Uw (2) This condition has been derived from Equation 1, that is to say, there was introduced in Equation 1 and k= 1, which is an important special instance.

Particular exemplified embodiments of the modulator arrangement of this invention are illustrated in Figs. 3 to 6. The circuit organizations are more particularly so designed that the carrier and/or the signal frequencies are absent in the amplifier output. Exemplifled embodiments Figs. 3 and 4, for instance, illustrate circuit organizations where the signal frequency is absent in the output.

A preferred exemplified embodiment adapted to suppress the signal frequency is shown in Fig. 3. Included in the cathode circuit of the amplifier tube V for carrier frequency are the nonlinear negative feedback resistances GII -and G12; these may consist more particularly of dry rectiers. furnishinga biasing voltage, required under certain circumstances for the rectiers. The resistances RI and R2 are included in the amplifier direct-current circuit. The drop of potential caused by the plate current across the resistances R2 and R3 may also serve for biasing the tube V. Alternating current is precluded from this circuit by means of the choke-coil D1' known in the art, while condenser C prevents the flow of the plate direct current across the non-linear resistances GII and Gl2. Owing to the differential winding of the signal transformer the signal w is suppressed in the grid and thus in the plate circuit.' 'Ihe amplifier tube V should preferably be of the screen-grid type.

In Fig. 3, the drop in the alternating-current path comprising condenser C and the network between C andA ground is in the circuit between the grid I and cathode I2 so that degenerative potentials are fed to the grid I0. 1 'I'he amplitude of the potentials fed baci-rv is controlled by controlling the conductivity of the non-linear resistances GII and GI2 and is done by the modulating potential w impressed on the transformer VU. RI is included in the grid circuit to supply a desired bias for the grid. v f

Also, -in exemplified embodiment Fig. 4 the signal frequency is suppressed in the output of the arrangement by using the differential transformer' V as shown. This embodiment contains only one non-linear resistance GI in the feedback path. In this circuit a single non-linear resistance GI is in the modulation potential degenerative feedback circuit. By using a push-pull circuit organization as shown in Fig. 5,it is also possible to suppress the carrier frequency as known in the prior art. The push-pull arrangement consists of the two amplifier tubes V and V. These also are preferably of the screen-grid type. Signal frequency, for example, is fed through transformer -VU to the rectiers GI and GI so that it is also absent in the output. The carrier frequency,however,

as shown in Fig. 6, could also be compensated by The resistances RI and R2 serve forl the use of a differential transformer T for the carrier frequency n and by introducing the resistance R in the output circuit. In the arrangement of Fig. 6 a point on the secondary winding of transformer T is connected to the grid I0 and a terminal is connected to the cathode return circuit and a second terminal to the anode I4 by way of resistance R.

What is claimed is:

1. In a modulation system, an electron discharge device having input and output electrodes including a control grid, an anode and a cathode, means forimpressing wave energy'to be modulated on said control grid, a modulated wave energy outputcircuit connected with said anode, a rectifier connected between said cathode and anode, a connection between said grid and cathode including said rectifier to provide in said tube a degenerative effect and means for modulating the degenerative effect including a source of modulating potentials coupled with said rectifier.

2. In a modulation system, an electron discharge device having input and output electrodes including a control grid, an anode and a cathode, means for impressing wave energy to be modulated on said control grid and cathode, a modulated wave energy output circuit connected with said anode and cathode, a non-linear resistance connected in an alternating current circuit between said cathode and anode, a circuit between said grid and cathode including said non-linear resistance to provide a degenerative effect in said tube and means for modulating the degenerative effect including a source of modulating potentials coupled with said non-linear resistance.

` 3. In a modulation system, an electron discharge device having an anode, a cathode and a control grid, a source of modulating potentials, a source of wave energy to be modulated, opposed non-linear impedances in a loop circuit common to connections between the cathode and the anode and between the cathode and the control grid to provide degeneration in said tube, an output circuit coupled to said anode and cathode, means for impressing the wave energy to be modulated on said control grid and cathode, and a differential transformer coupling said source of modulating potentials to said non-linear impedances by a circuit such that the provided degeneration is modulated and the modulating potentials are suppressed in said output circuit.

4. In a .modulation system, an electron discharge device having an anode, a cathode and a control grid, a source of modulating potentials, a source of wave energy to be modulated, a pair of rectiiiers connected in opposed relation by similar impedances, a connection between adjacent terminals of said rectiiiers and the cathode of .said tube, connections between adjacent termiode and a control grid, a pair of rectifiers con- I nected in opposed relation between the cathodes of said tubes, means connecting one of said recti- -iiers in a common portion of an alternating current circuit between the anode and cathode and grid and cathode of one of said tubes, means connecting the other of said rectifiers in a common portion of an alternating current circuit between the anode and cathode and grid ,and cathode of the other of said tubes, an output circuit coupling the anodes of said tubes in push-pull relation,

means for impressing wave energy ot carrier wave frequency in phase betweenvthe control grids vand cathodes ofy said tubes, whereby said carrier wave energy is suppressed in said output circuit, and -means for impressing modulating potentials in push-pull relation on said rectiers whereby the carrier wave is modulated and said modulating potentials are suppressed in said output circuit.

OTTO HENKLER. 

